1. Field of the Invention
The present invention relates to a near-field scanning microwave microscope, and more particularly, to a near-field scanning microwave microscope, which can minimize the bad influence of temperature or external environments thereon and enhance its sensitivity and resolution by connecting a probe to a dielectric resonator.
2. Description of the Related Art
An optical microscope for measuring the shape of a nanosize sample has a limited resolution due to a diffraction limit because it observes the shape of an object using light. That is, an object having a size smaller than the half of a light wavelength cannot be optically measured due to the diffraction limit. Accordingly, there has been developed a near-field scanning microwave microscope that can overcome the diffraction limit and thus measure an optical characteristic of an object having a size much smaller than a light wavelength. In the near-field scanning microwave microscope, light having passed through a microscopic aperture smaller than a light wavelength is scanned on a sample spaced apart from the aperture by a distance equal to or smaller than a diameter of the aperture, whereby the diffraction limit can be overcome because a near field spaced apart from a surface of the sample by a distance smaller than a light wavelength is not diffracted.
A study for a noncontact or nondestructive microscope using an evanescent or near field effect has been introduced as one field of a surface study after a scanning tunneling microscope (STM) and an atomic force microscope (AFM) were realized. Due to the development of optical microscope technology, the measurement of a characteristic of a sample through the existing optical method has been converted from a macroscopic view into a microscope view. Accordingly, a method for measuring a microscopic characteristic of a sample has been spotlighted as a new study field. Meanwhile, with the integration of various electronic components, a study for a physical characteristic of a fine structure is being highlighted as an important project. Specifically, the development of new measuring equipment capable of overcoming a diffraction limit becomes essential for understanding and measuring a physical characteristic of a fine structure.
A microscope using a near-field effect has been developed as one means for overcoming the diffraction limit. Specifically, with the integration of communication components, the development of a near-field microscope in a millimeter wave region or a microwave region has been required for a study on an optical characteristic of a fine structure of an integrated device.
An experiment for a near field using a microwave was first executed by Ash and Nicholls, and a near-field microwave microscope has been continuously developed and is being applied to various technical fields. Examples of methods for obtaining a near-field microwave image include a method using a coaxial cable resonator, a method using a stripline resonator, and a method using a waveguide slit.
FIG. 1 illustrates a conventional near-field optical microscope using a coaxial cable resonator, which is disclosed in “APPLIED PHYSICS LETTERS, VOLUME 75, NUMBER 20”.
In the above near-field optical microscope, a wave output from a microwave source 100 propagates through a coaxial cable resonator 103, and is transmitted through a probe formed at an end portion of resonator 103 to a sample 107 whose optical characteristic needs to be measured. A wave output from the probe 105 interacts with the sample 107, and is then again input through the probe 105 to the resonator 103. A microwave deformed by an interaction with the sample 107 is detected by a detector 110. In this manner, microscopic and optical characteristics of the sample 107 can be measured. Here, a reference numeral “102” denotes a directional coupler.
However, when the coaxial cable resonator 103 is used in the microscope, only an experiment in a microwave band can be performed due to a cut-off frequency caused by a structure of a coaxial cable. Accordingly, a resonance frequency of the near-field microscope must be limited to a specific frequency of the microwave band, whereby a limit exists in obtaining the maximum sensitivity. Also, since the coaxial cable resonator is constituted by two conductors, that is, inner and outer cylindrical conductors, only an experiment using a TEM wave can be performed. Accordingly, various wave modes for measuring various optical characteristics of the sample cannot be used in the above microscope. That is, since there exists a specific mode where an optical characteristic of a specific sample is well measured and since the coaxial cable can use only a TEM mode, the near-field microscope using the coaxial cable resonator can measure only limited kinds of samples.
Also, since the coaxial cable resonator 103 uses a frequency of a microwave band having a relatively long wavelength, its length inevitably becomes longer. That is, the coaxial cable resonator 13 inevitably has a length of about 2 m. Accordingly, a near-field optical microscope using a coaxial cable resonator is very large in volume, and is thus unsuitable for commercialization.
As another conventional near-field microscope, there is a microscope using a waveguide slit.
FIG. 2 illustrates a conventional near-field microscope using a waveguide slit, which is disclosed in “APPLIED PHYSICS LETTERS, VOLUME 77, NUMBER 1”. In the microscope shown in FIG. 2, a slit 115 is formed at one end of a waveguide 113, a substrate 120 is disposed below the slit 115, a sample 117 is disposed on the substrate 120, and light is irradiated from a light source 122 positioned below substrate 120. Here, a reference numeral “123” represents a shadow mask.
In the above structure, light irradiated from the slit 115 interacts with the sample 117, and is then input through the slit 115 to the waveguide 113. A microwave deformed by an interaction with the sample 117 is detected by a detector, whereby the shape and characteristic of the sample 117 can be measured. However, the conventional near-field microscope using a waveguide slit has drawbacks in that a light loss is increased and its resolution is degraded because light having passed through the slit 115 spreads.
Even a conventional near-field microscope using a improved waveguide structure is susceptible to external environments, is large in volume, cannot be easily assembled, and cannot measure various wave modes and various samples because a device for adjusting a distance between a sample and an end of a probe is not easily installed.